This is the first modern intellectual biography of the Scottish Covenanters’ great theorist Samuel Rutherford (c. 1600–1661). The central focus is on Rutherford’s political thought and his major treatise, Lex, Rex, written in 1644 as a justification of the Covenanters’ resistance to King Charles I. The book demonstrates that while Lex, Rex provided a careful synthesis of natural-law theory and biblical politics, Rutherford’s Old Testament vision of a purged and covenanted nation ultimately subverted his commitment to the politics of natural reason. The book also discusses a wide range of other topics, including scholasticism and humanism, Calvinist theology, Presbyterian ecclesiology, Rutherford’s close relationships with women and his fervent spirituality. It will therefore be of considerable interest to a range of scholars and students working on Scottish and English history, Calvinism and Puritanism, and early modern political thought.